Traditionally, testing of blood or other body fluids for medical evaluation and diagnosis was the exclusive domain of large, well-equipped central laboratories. While such laboratories offer efficient, reliable, and accurate testing of a high volume of fluid samples, they cannot offer rapid turn-around of results to enable more immediate medical decision making. A medical practitioner typically must collect samples, transport them to a laboratory, wait for the samples to be processed and then wait for the results to be communicated. Even in hospital settings, the handling of a sample from the patient's bedside to the hospital laboratory produce significant delays. This problem is compounded by the variable workload and throughput capacity of the laboratory and the compiling and communicating of data.
The introduction of point-of-care blood testing systems enabled practitioners to obtain immediate blood test results while examining a patient, whether in the physician's office, the hospital emergency room, or at the patient's bedside. To be effective, a point-of-care analysis device must provide error-free operation for a wide variety of tests in relatively untrained hands. For optimum effectiveness, a real-time system requires minimum skill to operate, while offering maximum speed for testing, appropriate accuracy and system reliability, as well as cost effective operation.
A notable point-of-care system (The i-STAT® System, Abbott Point of Care Inc., Princeton, N.J.) is disclosed in U.S. Pat. No. 5,096,669, which comprises a disposable device, operating in conjunction with a hand-held analyzer, for performing a variety of measurements on blood or other fluids. The disposable device, reproduced in FIG. 1, is constructed to serve a multiplicity of functions including sample collection and retention, sensor calibration and measurement. In operation, the disposable device is inserted into a hand-held reader or instrument, which provides the electrical connections to the sensors and automatically controls the measurement sequence without operator intervention. The disposable device includes an upper piece 90 and a lower plastic piece 12 in which are mounted a plurality of sensors 66 with electrical contacts and a pouch 60 containing a sensor-standardization or calibrant fluid. The sensors generate electric signals based on the concentration of specific chemical species in the fluid sample. A double-sided adhesive sheet 74 is situated between the upper piece 90 and the lower piece 12 to bond them together and to define and seal several cavities and conduits within the device.
In the '669 disclosure, a cavity 18 is located at the center of the device having a sealed pouch 60 containing calibrant fluid. A first conduit 24 leads from this cavity 18 toward the sensors 66. A second conduit 92 has an orifice at one end for the receipt of a sample while the other end of the tube terminates at a capillary break 96. A third conduit 94 leads from the capillary break 96 across the sensors 66 to a second cavity 20, which serves as a sink. The first conduit 24 joins the third conduit 94 after the capillary break 96 and before the sensors 66. A third cavity 22 functions as an air bladder. When the air bladder is actuated, the air is forced down a fourth conduit (see FIG. 2 of the '669 patent) and into the second conduit 92.
In operation, a fluid sample is drawn into the second conduit 92 by capillary action by putting the orifice at one end of the second conduit in contact with the sample. After the sample fills the second conduit, the orifice is sealed off. The pouch 60 containing the calibrant fluid is then pierced and the calibrant fluid flows from the cavity through the first conduit 24 to the third conduit 94 and across the sensors 66 at which time sensor calibration is performed. Next, the air bladder is actuated by the instrument forcing air down the fourth conduit to one end of the second conduit 92 which forces the sample out of the other end of the conduit, past a capillary break 96, and into the third conduit 94 and across the sensors 66 where measurements are performed. As this is done, the calibration fluid is forced out the third conduit 94 into the second cavity 20 where it is held. Once the measurements are made, the disposable device can be discarded.
The hand-held reader includes an opening in which the disposable device is received. After the disposable device is inserted into the reader, the reader engages the electrical contacts on the disposable device, ruptures the pouch, calibrates the sensors, actuates the air bladder to force the fluid sample across the sensors, records the electric signals produced by the sensors, calculates the concentration of the chemical species tested, and displays the information. Upon completion of the process, the user removes the device from the reader and simply disposes of it. The reader is then ready to perform another measurement, which is initiated by the insertion of another disposable device. Note that alternative cartridge fluidic systems that permit performing immunoassays and coagulation measurements using similar instrument format are described in jointly owned U.S. Pat. Nos. 7,419,821, 6,750,053 and 5,447,440, all of which are incorporated herein by reference in their entireties.
While use of the '669 invention, described above, is particularly advantageous in the point-of-care medical environment, there remains a need for single-use blood testing devices that are simpler to manufacture, assemble and use.